Means for reducing lightning interference in carrier telegraph circuits



June 21, 1932..

HORP 1, 3,6 5

V. MEANS FOR REDUCING LIGHTNING INTERFERENCE IN CARRIER TELEGRAPH CIRCUITS Filed June 19, 1930 15 other Recall/1'1 firm aches INVENTOR ATTORN EY Patented June 21, 1932 UNITED. STATES P TE T OFF VAUGHN P. THORP, 0F RIVER EDGE, NEW JERSEY, ASSIGNOR T0 AMERICAN TELE- M PHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK MEANS FOR REDUCING LIGHTNING INTERFERENCE IN CARRIER TELEGRAIH CIRCUITS Application filed June 19,

N tems, interference wit-h the reception of sig- 1'0 nals is frequently produced by voltage surges set up by lightning or other sources extraneous to the transmission lines. While the magnitude of the voltage resulting from lightning may be great relative to that of the signal impulses, such interfering voltages are generally of short duration, in fact, so short that they would not cause the operation of the receiving relay were it not for the presence in the circuits of elements that eflfec- 20 tively prolong the duration of such interfering voltages. The elements that effect such prolongation are the tuned circuits of the receiving branches, which, when excited by the interference voltage of great magnitude produce oscillations that are sustained sufficiently long to permit the building up of the operating current of the receiving relay to that value at which the relay will operate.

my copending application, Serial No. 462,380, filed June 19, 1980, I have disclosed means for reducing the shock excitation of the tuned circuits of the receiving branches of a carrier system by interposing in series with one of the tuned circuits a device whose resistance increases greatly when a negative voltage is applied thereto, thereby tending to dampen the tuning of that circuit by effectively introducing a very high resistance in series therewith.

This invention resides in means for effectively detuning a resonant circuit of a carrier telegraph system whenever the voltage impressed across such resonant circuit exceeds a fixed limit, the said detuning being ,transmissionf' circuit over which fnal voltage.

1930. I Serial No.l462,382.

efiected-by' the short-circuiting of either of the elements of the tuned circuit. 7

The invention will be clearly understood from the following description when read in t ing schematically a form of embodiment of the invention, 1 r p 'In the drawing, the line L represents a connection-with the attached drawing, showsignal voltages "of the telegraph channels are transmitted. That line is also exposed to sources of interferencethat may set up therein abnormal voltages whose magnitude'g'is the normal '55 relatively much greater than that of the sig the sending bus L, with which are connected the transmitting branch circuits. The line L is'also connected with the receiving bus The line L is connected with L, with which is connected a plurality of branches such as L and L The winding of the transformer associated with L has-its midpoint grounded in order to effect the operationof the detun'ing apparatus. Connected with the branch L is the series resonant circuit 1 that is coupled with the parallel resonant circuit 2. The junction between the inductance and the capacity of the series resonant circuit is connected to ground through a rectifier that is represented in the drawing as made up of a pair of copper oxide elements connected to ground. Those rectifiers therein shown are intended to pass current in the direction represented by the arro'w' whenever the voltageexceeds a predeabnormal voltages, the" normal ""signaling voltages of the frequencies representing the various channels will pass from the line L to the receiving bus L and will be impressed upon the various branches such as L and L The resonant circuit 1 will permit the flow of current therethrough of the particular frequency intended to be received by the branch L which current will produce oscillations in the resonant circuit 2. Those oscillations will be impressed upon the amplifier-detector 4 and will cause the current flowing through the relay 5 to effect its operation and to transmit an impulse over the loop L to the subscriber.

When aninterfering voltage wave is impressed by the transmission circuit L upon the receiving bus L it will in turnbe impressed upon each of the receiving branches. Accordingly,

a voltage of relativelyv great- June, 1930. l I l l v VAUGHN P. THORP.

magnitude will be impressed across these- A ries tuned circuit 1 that will effect the operation of one of the copper-oxide reotifiers, for example, the left-hand one, which, will establi'sh ,a circuit from the upper-conductor of L ethrough the inductance of the tuned circuit 1 through the left-hand rectifier to ground, thence to the midpoint ofthe winding of, the transformer associated with L and thence to the upper conductor of L thereby shunting the condenser lof the tuned circuitl andpreventing the building up of sustained oscillations that would eventually cause the operation of thereceiving relay 5. V w

With the reversal in polarity of the received interference voltage, the right-hand rectifier would be operated which would shunt the inductance of the tuned circuit 1 and in like manner, prevent the setting ;up of oscillatiOIlS. p i I It is desirable to point out that while copper-oxide rectifiers have been specifically mentioned in describing my invention, the invention is not limited to that rectifier, since other kinds of dry contactrectifiers maybe employed in the working of the invention.

'While the inventionhasbeen described as embodied in a particular form, it is capable of embodiment in other forms without departing from the-spirit andscope of the appended claims. g

. What is claimed is: V V v 1. In a carrier telegraph system, the combination' with a transmission circuitlupon which normal signal voltagesand abnormal interference voltages may be impressed, of a resonant circuit, comprising an inductance in series with a condenser, tuned to signal frequency connected with said transmission circuit, and rectifying means operative at a predetermined voltage to efie ctively shortcircuit both of the elements of the resonant circuit. g V

;2. In a carrier telegraph system, the com- 'bination with a transmission circuit upon whichnormal signal voltagesfand abnormal 

